Neon tubes and similar gas filled tubes are widely used in advertising and information display systems. In those systems, alternating current voltages are applied to electrodes located at opposite ends of a tube. If the voltage is high enough, the gas becomes ionized as electrons are attracted toward the positive electrode. In the course of such travel, they collide with neutral gas molecules in their paths causing the body of the gas to become ionized. The free electrons combine with positive ions and give off light as they do so.
Incandescent indicators, also widely used, are relatively expensive and contain large numbers of components. They are inefficient and require relatively large primary power sources. Furthermore, they are more costly to operate and maintain than gas filled tubes primarily due to bulb and control system failures.
Thus, luminous tubes are used primarily for both non-changing informational and on/off (flashing) applications. This limited application is principally due to the fact that a high leakage/reactance luminous tube transformer is required for each individual section of luminous tubing. Informational luminous tube indicators which change with time could be fabricated using large numbers of such transformers or using a mechanical switching network capable of dealing with the high voltage environment inherent in such transformers. Both of these approaches, however are economically impractical.
The problem involved in luminous tube systems using alternating current is to provide a high voltage in order to start the unit, and then abruptly to effect a lower voltage during the run interval in each half cycle. The transformers used in these systems operate in such a way that an initial high secondary voltage is reduced abruptly as high current flow is initiated. If too great a current is drawn, the voltage goes down almost to zero and high current can no longer flow. These transformers are generally described as having poor regulation.
It is advantageous to be able to provide luminous multi-tube indicators capable of changing informational content and operated from a direct current power supply by providing separately the ionization and sustaining voltages, thereby eliminating large luminous tube transformers and most of the associated high voltage wiring.
It is advantageous to be able to control individual luminous tube elements with a low voltage control signal and a mechanical switch or a solid-state (semiconductor) control device. This invention utilizes a luminous tube switch with integral low voltage control.
Accordingly, it is an object of this invention to provide a luminous multi-tube system having improved low voltage on-off switching.
Another object of this invention is to provide operation from a direct current power supply and provide static or multiplex element control.
It is yet another object of this invention to provide selectable on-off and brightness control in displays of various formats such as seven segment, dot matrix and other displays.